Ferromagnetic domain structures and spin configurations measured in doped manganite

Abstract

We report on measurements of the spin configuration across ferromagnetic domains in La 0.325 Pr 0.3 Ca 0.375 MnO 3 films obtained by means of low-temperature Lorentz electron microscopy with in situ magnetizing capabilities. Due to the particular crystal symmetry of the material, we observe two sets of independent ferromagnetic twin variants, one of which was pinned by crystallographic twinning. The spin orientation and configuration of the domains were measured quantitatively using electron diffraction and electron holography, and verified with structural modeling. The observed deviation of spin orientations from the expected 90°head-to-tail configuration across the domain walls was attributed to the variation in the domains' aspect ratios as a result of the demagnetization field. Our study provides important insight on how the spin configuration coupled with the magnetic structure and the crystal symmetry might affect the magnetoresistivity under an applied magnetic field in a strongly correlated electron system.

Competing two-phase coexistence in doped manganites: Direct observations byin situLorentz electron microscopy

“…Arrows pointing to the magnetic spin moments for single FM cells ͑a , b , c͒ are aligned collinearly to the zigzag Bloch 180°DWs across the ͑101͒ twin walls ͑dashed lines͒, thus minimizing total magnetostatic energy. 7 We notice that magnetic moments arranged in this way ͑parallel to local c axis within each twin lamella͒ always appear to be orthogonal to the charge-orbital ordering vectors ͑i.e., parallel to the local a axis of the same lamella͒, based on the TEM data shown in Fig. 3͑c͒.…”

“…5͑a͒ shows the typical zigzag domains for FM phase, greatly reducing magnetostatic energy in absence of stray fields. 7 The central area in Fig. 5͑a͒, outlined by a dashed square and magnified in defocused Fresnel ͓Fig.…”

“…Some of them are FM metals at low temperatures in zero magnetic fields, but upon heating they lose their magnetic order with a concomitant increase of several orders of magnitude in their electrical resistivity. One such a remarkable material in the manganite family is the mixed-valence compound La 5/8−y Pr y Ca 3/8 MnO 3 ͑LPCMO͒ that shows colossal magnetoresistance ͑CMR͒ and transport properties sensitive to y doping 2-4 including other intriguing phenomena [5][6][7][8][9] that are not well understood due to the system's complexity. Thus, even with fixed Ca doping ͑x =3/ 8͒ optimized for the magnetic Curie ͑T c ͒ point 1,10 the y tuning of La/Pr ratio in LPCMO may switch from the FMM ground state at y =0 toward the dominant COI state at y =5/ 8.…”

In situ transmission electron microscopy for magnetic nanostructures

“…Magnetotransport properties of magnetic nanostructures are essentially governed by the interaction of electron/spin current and the micromagnetic structure. And in situ measurement of magneto-electric properties in TEM magnetic imaging could help to describe this aspect [45][46][47]. Developments of TEM sample holders have enabled a new field of research in the study of functional nanomaterials and devices via electrical stimulation and measurement in TEM, particularly in TEM magnetic imaging [48].…”

Artifacts in magnetic spirals retrieved by transport of intensity equation (TIE)

“…Compared with electron holography (EH) which can also retrieve the magnetic information of the specimens in transmission electron microscopy (TEM), the advantages of TIE are the simpler experiment framework and faster data processing. Now TIE has achieved a widespread success in portraying domains within magnetic materials and devices [4][5][6][7][8]. The discovery of the so-called Skyrmions in some materials demonstrates the visualization advantage of TIE.…”